I imagine that this would be the typical carry out to the start of a search. Once at the scene, the SAR member could easily review his contents and leave a portion of it back in their vehicle. For example, if it was an urban search vs a field search, the contents required would be different. Again, same with the changing of the seasons. The SAR bag would have to be updated fairly often simply because the batteries for the radio etc. will only hold a charge for so long. All that said, it may be that his 55 lb bag gets pared down to 30 lbs in some situations.

I noticed he also has a fair bit of redundancy. You and I in our daily hiking packs might reduce that redundancy but when you are putting your life on the line in the possible rescue of another life then that is a reasonable assumption when outfitting the bag.

Regardless of the contents, I think his biggest asset is the radios. Keeping in contact with the other SAR members (often within visual range) is key to conducting wide scale searches.